The present invention relates to a discharge system for printed media sheets, including: a tray for the media sheets; rotating transport elements forming a discharge nip for discharging the sheets onto the tray; a guide plate having a surface for guiding the sheets to the discharge nip; and a rotating wheel containing bristles for guiding the sheets towards the discharge nip.
In printers and copiers, printed media sheets are frequently collected on one or more trays. The media sheets may be supplied, for example, from a stack of cut sheets, or may be continuously supplied from a reel and then cut into sheets. When the media sheets are supplied from a reel, they are often slightly curled. This effect becomes even more pronounced when the end of the coil on the reel is reached and the radius of curvature of the reel becomes smaller. But also when the media sheets are supplied from a stack of cut sheets, they may become curled during the printing process.
When the sheets are guided along the surface of the guide plate towards the discharge nip, in case of a curled sheet, a part of the sheet may stick out from the guide plate. This might prevent the leading edge of the sheet from being properly threaded to the discharge nip, possibly resulting in the sheet becoming folded. This danger cannot be avoided by an arrangement ensuring that the transport elements immediately engage a sheet when it is fed to the discharge system, for the following reasons. In case the sheet has been printed with ink, the ink might not be completely dry when the sheet is fed to the discharge system, so that the printed image might get blurred. Moreover, the configuration of the discharge system may require a certain length of the guide plate. For example, in a printer the tray may be positioned above the printing unit, and a curved guide plate is needed to reverse the sheet transport direction before the sheet is discharged onto the tray.
JP 08002775 A shows a paper discharge device in which a brush roller is arranged in the way of the leading edge of a sheet. Depending on the rotational direction of the brush roller, the brush roller guides the sheet to a paper through direction or to a paper discharge direction. In the latter case, the sheet is guided between the brush roller and a guiding surface which is curved away from the brush roller, and is then funneled through a space between the guiding surface and an opposing guiding surface towards the discharge rollers. However, a curled sheet might curl around the brush roller instead of being funneled towards the discharge rollers. Moreover, the paper discharge device is suitable only for dry sheets, because the sheet is conveyed between pairs of conveying rollers towards the brush roller, and because any surface of the sheet may be guided to a side of the brush roller where it gets into a sliding contact with an opposing wall.
From EP 0 407 151 A2, a similar sheet path selector with a bidirectionally rotatable brush wheel is known.
EP 0 407 152 A2 shows a sheet stacker in which fiber brushes and foam drive rolls are arranged on a rotatable drive shaft. The diameter of the fiber brushes is greater than that of the foam drive rolls, so that the fiber brushes urge a leading edge of a sheet being fed vertically downward toward a nip being formed between the foam drive rolls and a baffle which is bent away from the foam drive rolls. However, both sides of the sheet are in sliding contact with walls that guide the sheet towards the fiber brushes, so that the sheet stacker can only be used for dry sheets.
U.S. Pat. No. 4,824,091 A shows a sheet collection device in which a sheet is guided between opposing straight walls to a discharge opening, while the sheet is engaged between two nip rollers. Rotatable brushes are arranged at the discharge opening to wipe down against a trail end of a sheet that has been discharged onto a tray. The brushes are arrange coaxially with one of the nip rollers and force a leading edge of a sheet against the opposing wall and into engagement with the nip rollers. However, the brushes do not assist in threading the sheet into the entrance aperture between the opposing walls, so that a curled sheet might get folded there.